Based on the hydrolyzability of the diorganosilazane unit, diorganosiloxane-diorganosilazane copolymers have been proposed as water repellents for powders, fibers, and inorganic substrates. The following methods, for example, have been proposed for the preparation of diorganosiloxane-diorganosilazane copolymer:
(a) the preparation of diorganosiloxane-diorganocyclosilazane copolymer has been proposed by means of a co-condensation reaction between 1,3-bis(dimethyllithiumoxysilyl)tetramethylcyclodisilazane and diorganopolysiloxane having silicon-bonded chlorine at both molecular chain terminals (Journal of Paint Technology. PA1 (b) the preparation of diorganosiloxane-diorganosilazane copolymer has also been proposed by the reaction, in ammonia or primary amine, of a mixture of diorganodihalosilane and diorganosiloxane having silicon-bonded chlorine at both molecular chain terminals (Japanese Patent Application Laid Open (Kokai or Unexamined) Number Sho 60-145815 (145,815/1985). PA1 (A) a mixture or polymerization reaction product of PA1 (B) a cyclic diorganosilazane with the general formula ##STR2## where R.sup.1 is a monovalent hydrocarbon group, R.sup.2 is hydrogen or a monovalent hydrocarbon group, and n=3 or 4, PA1 (C) cesium hydroxide.
42 543 220,1970); and
However, the preparative method proposed in the Journal of Paint Technology article requires the use of difficult-to-handle butyllithium and can produce only block-type diorganosiloxane-diorganosilazane copolymer. The method proposed in Japanese Patent Application Laid Open Number Sho 60-145815 requires isolation of the product from the large quantity of ammonium chloride that is produced during the reaction process. In addition, this method again can produce only block-type diorganosiloxane-diorganosilazane copolymer.
In pursuit of the preparation of straight-chain diorganosiloxane-diorganosilazane copolymer in which the diorganosiloxane units and diorganosilazane units are randomly dispersed, the present inventor experimented with the equilibration polymerization of cyclic diorganosiloxane and cyclic diorganosilazane using basic catalysts such as sodium hydroxide and potassium hydroxide. It was found, however, that diorganosiloxane-diorganosilazane copolymer could not be obtained even with heating up to the boiling point of the starting materials.